This invention generally relates to magnetic resonance and more particularly to the measurement of electrical impedance, complex permittivity, and/or complex conductivity by the application of time-varying electric fields in an imaging volume (especially as it enables detection and evaluation of sample, e.g., human breast, pathology) or in a homogeneous sample volume (especially as it relates to industrial materials testing).
Magnetic resonance imaging of the human breast with and without gadolinium enhancement is a standard procedure in clinical medicine. S. A. Mirowitz et al., “Magnetic Resonance Imaging Clinics of North America,” W.B. Saunders Co., vol. 9, no. 2 (May 2001). Current techniques generally utilize the injection of e.g., gadolinium contrasting agents for breast imaging. The dielectric properties of breast carcinoma have been extensively investigated in vitro. A. J. Suroweic, et al., “Dielectric Properties of Breast Carcinoma and Surrounding Tissues,” IEEE Trans. On Biomedical Engineering, vol. 35, no. 4, pp. 257-263 (April 1988): Electrical impedance imaging in vivo is an FDA approved method for breast cancer detection. J. C. Hayes, “Electrical impedance images for breast gain FDA approval,” Diagnostic Imaging, pp. 19-20 (June 1999). U.S. Pat. Nos. 5,412,322, 5,757,187, 6,166,540 and 6,342,784 (incorporated by reference herein for all purposes) describe various effects produced by superposition of time varying electric fields in magnetic resonance devices. The production of gradients by an electric conduction current and the measurement of non-uniform conduction current density by magnetic resonance are described in the prior art. Holz, M. et. al., “NMR Measurements of Internal Magnetic Field Gradients Caused by the Presence of an Electric Current in Electrolyte Solutions,” Journal of Magnetic Resonance, vol. 40, pp. 595-599 (1980); G. C. Scott, et al., “Measurement of Nonuniform Current Density by Magnetic Resonance,” IEEE Trans. On Medical Imaging, vol. 10, no. 3, pp. 362-374, (September 1991). Complex permittivity is reviewed in other prior art. C. A. Balanis, “Advanced Engineering Electromagnetics,” Wiley & Sons, Section 2.8, (1989). Further background information can be found in other art. “The Transforms and Applications Handbook,” A. D. Poularikas (ed.), CRC Press, pp. 221-222 (1996).